The Rap was ordered from Thornycroft shipbuilding company, England, in either 1872 or 1873, and was built at Thornycroft's shipyard at Church Wharf in Chiswick on the River Thames. Managing a speed of , she was one of the fastest boats afloat when completed. The Norwegians initially planned to arm her with a spar torpedo, but this may never have been fitted. Rap was briefly used for experiments with a towed torpedo before finally being outfitted with launch racks for the new self-propelled Whitehead torpedoes in 1879. Her initial commanding officer was First Lieutenant Koren, who also designed the torpedo racks.